In high temperature particles on-line detection experiments, with the spherical SiO2 particles as the research object, a high-temperature test bed was set up for this research. By utilizing optical particle counter (OPC), the quantity and cumulative distribution of particles with different particle sizes were measured under the operating condition of 25?800℃. The spherical SiO2 dust particles were observed and analyzed by SEM and XRD. The results showed that the particle size of spherical SiO2 particles first decreased, then increased and decreased later with the increase of heating temperature, while the shape and size of the particles at the corresponding temperature did not change. The XRD patterns showed that the diffraction intensity of spherical SiO2 particles became smaller, and the diffraction peak was broadened and shifted approximately at 2θ=25.5o. The unit cell volume of spherical SiO2 particles increased first and then decreased. Thus, a conclusion can be drawn that the connection between SiO2 unit cell volume and crystal dielectric constant led to the change of the internal structure of SiO2 particles, as a result the refractive index of the particles crystal changed, thus resulting in a change in the refractive index, making the measurement results have 2~3 size error and the measurement accuracy was affected.